Limit switch



C. R. KELTY LIMIT SWITCH Dec. 9, 1930.

Filed Feb. 8, 1926 2 Sheets-Sheet 2 Vv[Pu/02130 21 nZa/aze@ R. y

Patented Dec. 9, 1930 PATENT OFFICE CHARLES R. KELTY, F MILTON, MASSACHUSETTS LIMIT SWITCH Application filed February 8, 1926. Serial No. 86,679.

This invention relates to electric switches and the particular example thereof chosen for purposes of illustration is a so-called limit switch adapted to interrupt the electric circuit by which the motion of some mechanism is controlled when that mechanism reaches the desired limit of travel. One important purpose of the invention is to provide such a switch in which the contact is broken with a sudden, rapid movement.

As an example of the invention to permit it to be more readily understood I shall herein illustrate and describe as an example thereof a limit switch such as might be used to control the motion of a mechanically actuated valve although obviously the structure is not limited to such an application.

In the following description of such an exemplary embodiment of the invention I shall refer to the illustration thereof in the accompanying drawings, wherein:

Fig. 1 is aside elevation of the switch;

Fig. 2 is a section on the line 2 2 of Fig. 1

Fig. 3 is a detail of Fig. 2 on an enlarged scale;

Fig. 4 is an enlarged detail of a portion of Fig. 2 but with the moving brush in a somewhat dilferent position;

Fig. 5 is a section on the line 5 5 of Fig.

1 on an enlarged scale; and

Fig. 6 is a wiring diagram.

Referring to the drawings, I have therein shown the switch as organized in a suitable casing embodying end plates 7 which may be held in spaced relation by side pieces 9, certain of which, as best shown in Fig. 5, may be provided with glazed windows or sight openings 11 to permit inspection of the mechanism of the switch while protecting the same from exterior influences.

Journalled in the two end plates 7 is a screw 13 which is adapted to be driven in timed relation with the mechanism the movement of which is to be cont-rolled as, for example,

by means of the worm wheel 15 on said screw driven by the worm 17 taking motion from some part of that mechanism. On the screw 13 are suitable nuts 19 which are traversed by the screw and carry moving contacts or brushes 21 and 21a adapted to cooperate with relatively stationary contacts, this screw and nut mechanism being an example of a suitable brush traversing device.

In the example of the invention shown there are two brushes, one controlling movement of the governed mechanism in one direction, for instance, the upward or opening movement of a valve, and the other its movement in the reverse direction, as a downward or closing movement. As these brushes and their cooperating mechanism are closely similar one to the other, I shall first limit my description to one alone and for this purpose shall consider the brush 21 shown in full lines in Fig. 1 and at the left in Fig. 2 and 65 which is adapted to control the valve or other device in its upward movement and which provides for the closing of a circuit which is interrupted at an upward limit of travel of the brush. 7

Referring particularly to Figs. 2 and 5 of the drawings, I have there shown the screw 13 as enclosed in a tube 23, preferably of insulating material, seated at its end in recesses or seats 25 in the two end plates 7. This tube 75 may be provided with longitudinal slots through which project laterally extending arms 27 of the brush holders mounted on the nuts 19, the nuts being thus restrained from rotation and forced to move along the screw 50 as the latter rotates, carrying with them the brushes 21 and 21a at the exterior of the tube. Each brush cooperates with a suitable stationary contact at the exterior of the tube and herein they are in the nature of bridge` contacts, the brush 21, for example, being adapted to connect the two long track-like` contact members 29 and 31 which may conveniently be mounted on the exterior of tube 23 as shown in Fig. 5. Referring to Fig. 1, the brush 21 moves from a lower limit substantially as there shown up between the contacts 29 and 31 and when it passes beyond their upward extremities breaks the circuit.

For a purpose which will be hereinafter more fully explained the exit end of the passage deiined by the two contacts 29 and 31 is narrowed herein by defiecting inwardly at 33 the ends of the surfaces on which the brush travels into the path of the brush so that the latter must be forced through the narrowed exit opening. This inward deflection may be provided for by embossing the contacts inwardly, best illustrated in Fig. 4, providing for a slight outward flaring at the opposite side to facilitate the re-entry of the brush between the contacts when it travels downwardly, viewing Fig. 4, from a position above the contacts 29 and 31 to enter between them again.

The arrangement and mounting of the brush preferably provides for a storing of power during the latter partof its travel, which power may be released to provide for a sudden and rapid movement of the brush away from its contacts and for this purpose it may be resiliently mounted on the arm 27, the return or reaction of the resilient means providing for the rapid travel of the brush as it passes olf the contacts. Such resilient mounting is conveniently effected by means of a spring and in the present example, since the brush 21 is pushed upwardly through the narrowed opening at the upper ends of the contacts 29 and 31, a compression spring is utilized and I have herein shown (see Fig. 3) the brush contact proper 21 as mounted on a base 35 seated on spring 37 interposed between the same and the arm 27 and adapted to be forced downwardly7 against the force of the spring over the insulating sleeve 39 which is embraced by the spring, this sleeve being secured to arm 27 by screw 41.

To permit the brush to be forced through the narrowed exit opening between contacts 29 and 31 provision is made for a lateral yielding and herein the brush itself is transversely compressible and it may be constructed, as shown in Fig. 4, of two bent arms presenting elbows to rub along the contacts 29 and 31 and which provide on either side of the elbows converging surfaces. Thus, when the brush moves upwardly, viewing Fig. 4, toward the position shown the free ends of the arms pass freely through the narrowed opening between the inward deflections 33 and on further upward movement of the brush it is forced between such deflections, the two arms bending together to permit such action. On reverse movement the lower converging surfaces of the arms cooperate similarly with the flaring terminals of the contacts 29 and 31 to facilitate re-entry of the brush therebetween.

It will be understood that as the brush 21 travels upwardly and reaches the position illustrated in Fig. 4, a resistance to its further progress will be offered and before it can be forced through the narrowed eXit opening it will be retarded relatively to the arm 27 which carries it and the spring 37 will be compressed. Then as it is forced through the opening, the arms of the brush yielding to permit this action, the spring 37 will be relieved from stress and the brush will be moved upwardly and away from the contacts 29 and 31 with a sudden rapid movement independently of the movement of the arm 27 which carries it. A quick and positive interruption of the circuit is thus provided for.

In the embodiment of the invention shown the brush 21 passing upwardly from between the two contacts 29 and 31 is carried between and seats on two contacts 43 and 45 which may be utilized as hereinafter described to continue in the same direction the motion of the apparatus governed when it is so desired. The mechanism will be more fully described hereinafter but briefly it may be said that the contacts 43 and 45 are connected in parallel with the contacts 29 and 31 but in a circuit which includes a normally open switch.

In order to permit proper positioning of the brush 21 relative to the contacts and to the traversing screw 13 the arm 27 may be threaded, as shown in Fig. 3, on the exterior of the nut 19 which carries it and is provided with a set screw 47 adapted to enter one of a pair of diametral slots or keyways 49 in the nut to clamp the arm in adjusted position thereon. The nut 19 is conveniently provided with spanner holes 51 by which it may be manipulated.

The brush 21a seen at the right of Fig. 1 is adapted to control the movement of the valve or other mechanism in a downward direction and the brush is similar to the brush 21 and similarly mounted except that it is reversed in position and it travels between two contacts 53 and 55 which are deflected inwardly adjacent their lower ends to provide a narrowed eXit. The length of the contacts is such that after the brush 21 has left the contacts 29 and 31 in its upward movement the brush 21a is still engaged between the contacts 53 and 55 and conversely when the brush 21a has passed downwardly beyond the contacts 53 and 55 the brush 21 is still in position between contacts 29 and 31.

rIhe electrical operation of the switch will be clear from Fig. 6 in which it is shown diagrammaticallyv as associated with a reversible electric motor 57 having a separately excited field circuit 58 adapted to be energized from the power line 59 through the reversing switch 61. For convenience I shall describe the operation of the parts as if they were controlling the movement of a valve. The parts are shown in their lowermost position with the brush 21a free of the down contacts 53 and 55. The switch 61 being properly manipulated, current passes through wire 63 to contact 29, through brush 21 to contact 31 and through wire 65 to motor 57 and thence through the normally closed push-button switch 67 and the wire 69 to the positive side of the line. The motor is thus operated to lift the valve and its travel may be interrupted at any desired position by opening the switch at 67. Assuming, however, that this switch is not opened, the

`brush 21-passes beuween the inwardly defiected Aupper-.ends of the contacts l29 and 31,

vopen switch such as the push-button switch 69a so that'znormally when t-he brush passes from between the contacts 29 and 31 energization of the.y motor 57 ceases. If desired,

=however, movement of the motor in the same direction as before may be continued by closing the switch 69a. Thus, in the case of the valve suchmovement may be effected if it is desired' to lift the valve out of its casing.

As the brush 21 advanced up between the contacts 29 and 31 the brush 21a entered between the contacts 53 and 55 which, however, were notin the circuit then closed by the switch 61 and after the brush 21 passed beyond its contacts the brush 21a was left between the upper end of the contacts 53 and 55. If the switch 61 is now reversed, current flows through the motor 57 in the opposite direction through wire 71 to the motor, thence through the switch 73 to contact 55, brush 21a and contact 53 and wire 75 to the negative side of the line. The motor will rotate in the opposite direction and the valve will be lowered, the'two brushes both travelling downwardly. The downward movement of the valve or other mechanism may be arrested at any desired point by opening of the switch 73 but if this is not done, the movement will be continued until the brush 21a passes between the lower ends of the contacts 53 and 55 and is disengaged therefrom with the sudden movement provided for by the construction described. The supply of current to the motor 57 is then interrupted and the parts have resumed the position shown in Fig. 6.

I have described in detail the embodiment of my invention illustrated by way of example in the accompanying drawings. It will be understood that the detailed nature of this description has had for its object making clear the features of construction which are illustrated in the accompanying drawings of an embodiment of the invention. Obviously the construction might be widely varied without departing from the principles of the invention and therefore the full nature of the description is not to be taken as in any way a limitation on the scope of the invention. exemplified by the specific disclosure which I have made and which I claim as new and desire to secure by Letters Patent I shall express in the following claims.

Claims:

l. In a switch, opposed extended Contact The features of novelty,

surfaces, a brush to travel therebetween,ends of the surfaces being deflected toward each other across the path of the brush to resist travel of the same, one of said elements being laterally yieldable to permit the brush to pass said ends, means to advance the brush and a resiliently yieldable device supporting the brush therefrom. Y

2. In a switch of the class described in combination with a feed screw, a nut traversed thereby, a brush comprising a pair of opposed elbowed arms, a spring interposed between the brush and the nut, a pair of contacts between which the elbows of said arms travel, said contacts converging at one end to provide a narrowed outlet.

3. In a switch of the class described in cornbination with a feed screw, a nut traversed thereby, a brush comprising a pair of relatively compressible elbowed arms, a spring interposed between the brush and the nut, a pair of contacts between which the elbows of said arms travel, said contacts converging at one end to provide a: narrowed outlet.

4. In a switch in combination. opposed extended contacts, a feeding device, cooperating contact springs supported from said device betweensaid opposed contacts and means adjacent the circuit breaking ends of said extended contacts to momentarily stop movement of the contact spring thereby to tension said spring.

5. In a switch,-a brush comprising elements normally definitely spaced in opposed relation but relatively yieldable, contacts comprising surfaces on which said elements travel in normal position but having portions differently spacedy to resist travel; of the brush and cause said elements to yield to permit passage of the brush andmeans -fortraversing the brush comprisinga resiliently yieldable driving connection.

6. In a switch, a pair of opposed extended contact surfaces, a brush com risinga pair of relatively resiliently yielda le contacts to travel therea'long, ends of said surfaces being contracted to displace said contacts against their yielding resistance, means for advancing the brush along said surfaces and means rendered effective by the resilient return of said contacts when the brush passes the said contracted ends to effect an abnormally rapid movement of the brush in its direction of advance.

7. In a switch, a pair of opposed contacts defining between them a passage with a narrowed outlet, a laterally compressible brush travelling between such contacts and amounting therefor comprising resilient means which is stressed by the forcing of said brush through said passage.

8. Ina switch, a contact couple, one element thereof being a pairof contacts defining between them a passage with a narrowed out- Yietand the..othere1ementbeng.a brush to` travel between said contacts` one of said elements being yielding to permit the brush to pass through said outlet and a mounting for the brush comprising a resiliently yieldable device which is stressed by the forcing of said brush through said passage.

9. In a switch.r a first contact couple, one element thereof being a pair of contacts delining between them a passage with a narrowed outlet and the other element being a brush to travel between said contacts, one of said elements being yielding to permit the brushhto pass through said outlet, a mounting for the brush comprising a resiliently yieldable device which is stressed by the forcing of said brush through said passage and a second couple comprising contacts beyond the contacts of the first couple on which said brush is seated by the reaction of said means.

10. In controlling means for a reversible motor, a pair of brushes and means for traversing the same, contacts with which the brushes cooperate respectively, the first brush adapted to travel past its contact, the second remaining engaged, the second brush adapted to travel past its contact, the first remaining engaged, and an auxiliary current conducting contact with which the first brush engages after leaving its contact first mentioned, whereby the operation of the motor may be continued in the same direction.

11. In a switch, in combination, a. brush holder, feeding means therefor, brushes carried b v said brush holder, and means for positively adjusting said brush holder to advance or retard the point of contact of said brushes.

12. In a switch, in combination, a screw, a. nut threaded thereon, a member having a brush-holding arm extending from said nut, elements between which said arm projects for travel therebetween lengthwise of the screw and a contact carried thereby to cooperate with the brush.

13. In a switch, in combination, a screw, a nut threaded thereon, a tube surrounding the same and having a longitudinal slot, a brushholding arm projecting from the nut and passing through said slot and a Contact mounted on the exterior of the tube to cooperate with the brush.

14. In a switch, in combination, a screw, a nut threaded thereon, a tube of insulating material surrounding the same having a longitudinal slot, a brush-holding arm projecting from the nut through said slot and a contact exterior to the tube to cooperate with the brush.

15. In a switch, a casing, a screw journalled in the ends thereof, a nut thereon, a laterally projecting brush-carrying arm on the nut, an insulating structure extending between the ends of the casing and enclosing the screw, said structure providing a longitudinal passage receiving said arm, a Contact carried by the exterior of the structure and a window in the side of the casing to provide for inspection of said part.

16. In a switch, a pair of end plates, a screw journalled therein, said plates having seats, a tube extending between said seats and encircling the screw, said tube having a 1ongitudinal slot, a nut on the screw having a brush-holding arm projecting through the slot and a contact mounted exteriorly on the tube to cooperate with the brush.

17. In a switch of the class described in combination with a feed screw, a nut traversed thereby, a brush comprising laterally opposed resilient arms, a spring interposed between the brush and nut, a pair of contacts between which said laterally resilient arms travel, said contacts converging at one end to provide a narrowed outlet.

In testimony whereof I have signed my name to this specification.

CHARLES R. KELTY. 

